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How-to Tip: Add Four Additional Auxiliary Inputs to Your Stereo System for Only $12.34!

By Howard Charles Best, October 15, 2001

(LLBest.com)

Picture showing the passive mixer.

If you’re like me, you’ll want to play your computer through your high fidelity stereo system in order to get the maximum possible sound quality. The problem is, my stereo system has only one auxiliary input, and I have two computers, a portable MP3 CD player, and a VCR, all of which I want to be able to play through my stereo system. Another requirement is that I not have to switch anything and that I be able to hear the sound from all 4 sources simultaneously. I also require that absolutely no noise be added. This sounds like a tall order, and a professional mixer costing hundreds of dollars comes to mind.

Please keep in mind that you cannot connect audio outputs in parallel because they will load each other down, and can even cause your equipment to be damaged.

My solution to this “tall order” is actually extremely simple, and it’s called a passive mixer. In other words, a mixer with no amplification. My passive mixer project was put together using only $12.34 worth of parts. It has five stereo inputs, so at present, I have one extra input for future expansion.

My passive mixer does not include volume controls, but three out of the four devices have their own volume controls. Only the VCR lacks a volume control. Therefore, I adjust the volume of my stereo system to match the VCR’s output, and then adjust the volume on the MP3 player and the two computers to the same level as the VCR.

This system works extremely well, and I am more than satisfied with it’s performance.

Parts you’ll need to build the passive mixer.

Parts list including Radio Shack catalog numbers:

(1) 270-1804 6"x2"x1" Project Box $2.89 (3) 274-0346 Pkgs of 4 - Shielded Phono Jacks 8.07 (2) 271-1335 Pkgs of 5 - 10K, 1/4 Watt Resistors 1.38 ------ $12.34 Also needed: (4) 1" pieces of “spaghetti tubing” ...or insulation stripped from hook-up wire.

The “project box” comes with both a plastic and an aluminum top. Only the aluminum top is needed:

Parts which are not needed.

You’ll also need some tools.

List of required tools:

Awl or center punch Combination square Drill bits: 1/16", 1/8", 1/4" and 3/8" Drill, Electric, 3/8" or 1/2" Hammer Long nose pliers Nut driver, 9mm Screwdriver, #1 Phillips Side cutters Soldering gun or iron Solder, radio/TV type Wire strippers

Schematic:

The left and right channel circuits are identical.

Step-by-step assembly instructions:

1. Score the underside of the aluminum top with the

tiny awl that comes with your combination square.

2. Using a hammer and an awl or center punch, make

indentations where the phono jacks are to go. I used

3/4" centers vertically and 7/8" centers horizontally.

3. Drill 1/16" holes and then enlarge them to 1/8". This

is important for accurate positioning of the holes.

4. Enlarge the holes to 1/4" and then use a 3/8"

drill bit to gently smooth the edges of the holes.

5. Tighten the phono jacks using a 9mm nut driver.

6. Solder the resistors to the phono jacks. Two of the resistors

need insulated leads to prevent shorting. I stripped some

insulation off of some “hookup” wire for this purpose.

7. The finished product. Please note that I

circled the output jacks with a Sharpie pen.

Questions, comments and suggestions are welcome.
Howard Charles Best ()

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